Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with agraphical user interface in accordance with an embodiment; and,

FIG. 2 is a front view of a display screen or portion thereof with agraphical user interface in accordance with an embodiment.

The rectangular broken-line perimeter in FIGS. 1 and 2 showing a displayscreen or portion thereof are for environmental purposes only and formno part of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, substantially as shown and described.